1. Field of the Invention
The present invention relates to an optical data recording disc on which video or audio data signals are recorded with the aid of a laser beam.
2. Description of the Prior Art
A conventional optical data recording disc has a positive type, photo-resist layer formed on the surface of a glass disc which has been optically polished to a thickness of .lambda./4n, where .lambda. is the wavelength of the reproducing light source, and n is the refractive index of the reproducing disc material. A laser beam is applied onto the recording disc, and the laser beam is modulated with data signals. Subsequently, the recording disc is developed, which results in the formation of pits in the photo-resist layer surface which correspond to the data signals. Accordingly, the recorded signals cannot be reproduced simultaneously with or immediately after the signal recording because it is necessary to develop the recording disc separately. As a result, if a failure occurs during the recording operation, e.g., the recording device fails to operate properly or the disc is defective, the failure cannot be detected until the recording disc is developed. Therefore, when a failure occurs, useless work continues to be performed, and this is not cost effective.
Japanese Patent Application Publication No. 65340/1981 discloses an optical recording medium which has a three-layer structure, the first layer being a light reflecting layer, the second being a light transmitting layer, and the third being a light absorbing layer. The light transmitting layer is made of an organic material which is molten, decomposed or sublimated at a temperature of at least 300.degree. C. below a melting point of the material of the light absorbing layer. A recording light beam applied to the recording medium is absorbed by the light absorbing layer and melts the light transmitting layer so that the light absorbing layer is pushed upward. Accordingly, the data are recorded in the form of bubbles. The light reflecting layer reflects the recording light beam, thus increasing the sensitivity of the recording medium.
Using the recording medium described above, data can be recorded and simultaneously reproduced. However, because of the three-layer structure, a number of manufacturing steps are required to produce this recording medium, thus resulting in unduly high manufacturing costs.